Around season 2 I just stopped....I was done so many times though.
-Ninjas...really turning out to be samurai's.
-Rock Lee, the baddest muhfukker, goes full blown Akuma, and it never happens again nor do they even give him any spotlight.
-Naruto suffered from the protagonist curse in all of anime....except that, he's a living god....quite literally.
-Killed of Jiraiya, probably the move that had me drop the manga for a while.....they tried the same with Kakashi, but the fans weren't having it.
-Infantile writing. To me, this is the biggest problems with manga/anime. A lot of these guys didn't take one class of writing. Not that you should, but you can tell these guys are too self indulged on thinking about whats "cool" and less about what makes sense. Toriyama was victim of this very thing...except he basically just made it fight fluff anime. The Sasuke arc was probably the worst writing in anime history. All that Naruto went through, Orichimaru living on through Sasuke, and eventually it all culminating to them being friends, was probably the biggest fail ever. So Naruto doesn't get with Sakura, even though that was bae for two seasons, and she then proceeds to marry and has the baby of the dude who was going to kill her and the entire village....
The shyt right there, is just too dumb.
-Killing off Neji - So basically, anyone who deemed cool by the fans, died. From Jiraiya, to Asuma. I get that this is basically the imaginings of a guy who never took a writing class, but his beta is showing.
So many more, but this is the crux of it. Bad writing + Sasuke being the Mary Sue/Big Bad/redeemed tortured soul.